Free sex behavior among teenagers is increasingly worrying and needs special attention from all parties. One of the driving factors for students to engage in free sex is influenced by several factors. Among them are the friend factor, the technology factor and the parent factor. The purpose of this study is to determine the factors that influence the behavior of adolescents to have free sex in STIKes Bina Sehat PPNI Kab. Mojokerto. The design of this research is descriptive. The population in this study were all level 2 adolescents at STIKes Bina Sehat PPNI Mojokerto Regency, totaling 181 active students. The sampling technique of this research is total sampling. The sample in this study was the entire population of students at level 2 STIKes Bina Sehat PPNI Mojokerto Regency, amounting to 181. The data analysis was presented in the form of percentages and tables. Based on the research obtained results that most respondents have free sex behavior based on friend factors with bad criteria as much (60.8%), The results of technology influence research obtained results as much as 37.6% and parental influence as much as 45.9%. The behavior of adolescents who have high free sex is influenced by the friend factor. In adolescence they usually have their own characteristics among their peers and it is not surprising that teenagers are easily affected by their peers. Peer influence makes teenagers have a tendency to use peer norms rather than existing social norms.